Secondary battery, which is mounted on, for example, a human-driving vehicle with an auxiliary power source, is recharged by means of a battery charger connected to a domestic electrical outlet. Conventionally, Ni-Cd cells or the like are used for such a secondary battery.
In the charging of the Ni-Cd battery, the battery voltage is measured for controlling the charging. After the start of the charging, the battery voltage rises increasingly, and then becomes constant. After that, the voltage of the secondary battery B rises again and peaks once before the secondarybattery B is fully charged. After the peak, the voltage-drops continuously. When it is detected that the voltage of the secondary battery B drops by .DELTA.V from the peak value, the charging is controlled to be finished.
In addition to such a measurement of the battery voltage, the charging time may be counted by a timer. In this case, the charging is finished when the voltage-drop .DELTA.V has been detected, or when a prescribed time has passed.
It is known that charging of the Ni-Cd battery is affected by temperature very much. Therefore, in charging of the battery, it is possible that the lifetime of the battery is shortened if an appropriate control is not carried out on the basis of the temperature of the battery. However, such a charging method according to the battery temperature has not yet been proposed in fact.